So just got a very quick response to an email I sent, from Ryan at ReefPhoto (what a guy!....
) - anyway here is the scoop as I understand it (granted I don't understand everything so allow for that please):
The d300 in the ND30 fits different than the d200 in the ND20. The way Ryan put it:
"I knew they were planning to tighten the tolerance on how the camera is captured at the top of the housing, and the camera tray locking mechanism , and did notice that this was a little stiffer. IE, on ND20 you dropped it in and locked it, where on ND30 you drop it in, push on the tray, then you can lock it."
then he added:
"If any adjustment is in order I'll let you know, and get that taken care of".
But note I don't know if there is any adjustment needed quite yet because I haven't used it much? Unfortunately I can't dive it a lot for a few more weeks.
I think it will be fine, I just miss the wonderful way my d200 fit in my ND20 -- the ND30/d300 is just different, a little tougher to insert in the housing and could possibly need adjustment?
Again - disclaimer - this is just my experience and there are much more experienced people out there to seek advice from if you want help with or want to purchase an ND30 or used ND20 for that matter. Please contact someone like Ryan Canon or someone else on this forum who has used the ND30 a lot for expert info and advice.
Best and more to come, Carol